Resistance unit and method of making same



Nov. 8, 1949 w. M. KOHRING 2,487,057

RESISTANCE UNIT AND METHOD OF MAKING SAME Filed F81). 23, 1946 2Sheets-Sheet l l9 l6 2 I7 I H 6 4 INVENTOR.

WILBUR NLKOHRING AT TORNEYS Nov. 8, 1949 w. M. KOHRING 2,487,0 7

RESISTANCE UNIT AND METHOD OF MAKING SAME Filed Feb. 23, 1946 2Sheets-Sheet 2 22 f 1 by 32 INVENTOR.

WILBUR M. KOHRING ATTORNEYS Patented Nov. 8, 1949 U ITED STATES PATENTOFFICE RESISTANCE UNIT AND METHOD OF MAKING SAME Wilbur M. Kohring,Lakewood, Ohio Application February 23, 1946, Serial No. 649,559

3 Claims. (Cl. 201-64) The present improvements while relating generallyto resistance units, irrespective of their application, have moreparticular regard to resistance units such as are utilized incommunication and signalling systems, both wire and radio, in which theelectric currents involved are of relatively low amperage.

Great numbers of such units are, for example, required in connectionwith modern radio transmitting and receiving equipment so that the costthereof is of important consideration. At the same time it is quiteessential that such resistance units should be of sturdy construction,not subject to deterioration in use, and capable of convenientinstallation.

Accordingly, one principal object of the present invention is to providea unit which will be of exceedingly simple construction and yet becapable of standing up under severe conditions of use. A further objectis to provide a unit which is adapted for manufacture by automatic orsemiautomatic methods, thus permitting quantity production andcorresponding reduction in cost.

To the accomplishment of the foregoing and related ends, said invention,then, consists of the means hereinafter fully described and particularlypointed out in the claims.

The annexed drawing and the following description set forth in detailcertain methods and products exemplifying the invention, such disclosedprocedures and products constituting, however, but several of variousapplications of the principle of the invention.

In said annexed drawings:

Fig. 1 is a side elevation of one form of my improved resistance unit;

Fig. 2 is a longitudinal central section thereof on a somewhat largerscale;

Figs. 3 and 4 are transverse cross-sections thereof on the same scale asthat of Fig. 2, the planes of such sections being indicated by the lines3--3-and 44 respectively on said figure;

Figs. 5 and 6 are cross-sectional ,views both taken on the planeindicated by the line 3-3 on Fig. 2, but on a still larger scale inorder to better illustrate certain modifications which may be employedin order better to secure the terminals of the unit to the body member;

Fig. 'I is partly a side elevation and partly a sectional view of amodification of the unit;

.Fig. 8 is a central longitudinal section of such modified form;

Fig. 9 is a perspective view of one end of such modified unit withportions broken away in order better to illustrate the construction;

Fig. 10 is likewise a central longitudinal section of still anothermodified form of my unit;

Fig. 11, like Fig. 9, is a perspective view of one end of such unit witha portion thereof broken away; a

Fig. 12 is a central longitudinal section of still another modifiedconstruction of my unit;

Fig. 13 is a side elevation, more or less diagrammatlc in character, ofan apparatus designed for use in assembling resistance units of theforms illustrated in Figs. 1 to 6 inc.;

Fig. 14 is a transverse sectional view of such apparatus, the plane ofthe section being indicated by the line "-44 Fig. 13;

Fig. 15 is a view of a detail of the apparatus as shown in Fig. 14 butshowing a different operative position of certain parts of theapparatus;

Fig. 16 is a transverse sectional view of another portion of theapparatus, the plane of the section being indicated by the line |6--i6on Fig. 13;

Fig. 17 is a transverse view of the portion of the apparatus illustratedin Fig. 16, the plane of the section being indicated by the line i'I--llon said figure; and

Fig. 13 is a view, more or less diagrammatic in character, illustratingthe manner of assembling certain of the parts that enter into theseveral modified forms of the unit shown in Figs. 7 to 12 inc.

Referring to the form of resistance unit illustrated in Figs. 1 to 6inc., the body 1 thereof consists of a tubular member of insulatingmaterial such as molded resin, porcelain or other ceramic material, thesize of said member, and more particularly the superficial area of theaxial bore 2 that extends therethrough, being varied to suit therequirements for which the unit is designed. The surface in question hasapplied thereto (Fig. 2) a thin coating 3 of graphite, amorphous carbon,or like conducting material. The latter may be applied in various ways,for example in the form of a paste made by intermixing such graphite orthe like with a suitable vehicle, such as a liquid resin, varnish orsimilar binder. While such coating composition may be applied in anysuitable manner, as by dipping or spraying, it will preferably beapplied in the manner and using the apparatus hereinafter described soas to insure uniformity in the coating with correspondingly closelimitation of the specific resistance which such coating will providewhen connected with the terminals 4, 4 of the unit.

The latter, which will consist of any suitable metal, preferablycomprise short lengths of wire,

the inner ends 5 whereof have a diameter slightoneness 3 ly larger ththat of bore t in the body oi the unit. Such terminals d are alsopreferably, although not necessarily, formed with integral up= setshoulders ii a short dis from the r ends thereof so as to insure thecorrect location of such ends when the to are r "w! in the body, or inother words, insure uniformity in the longitudinal extent of the coatingit which lies between and electrically connects such ends. As a resultthe resistanceatiorded by such coating may be accurately gauged. Inorder to insure a firm connection between the ends B of terminals 4where they are thus fitted into the bore 2 of the body of the unit, suchbore may be formed with angular longitudinally extending ribs 7, asillustrated in Fig. 5, or with similar longitudinally extending angulargrooves I, as illustrated in Fig. 6. Accordingly. remem bering that thediameter of such terminal ends is equal to or slightly greater than thatoi the bore, when the former are forcibly inserted into the latter themetal composing the terminals will either be cut by the ribs :7 .orforced into the grooves 8 so as to provide a very firm, serratedconnection between the two parts in question. It will be understood thatthe coating 3 as initially applied to the bore 2 extends substantiallyto the respective ends thereof, and the te was. when thus forced intoposition in the body of the unit will necessarily have good electricalcontact with such coating.

Before describing the preferred method for assembling the parts of theresistance unit de-= scribed above, it will be convenient to describethe several modified dorms illustrated in Figs. 7 to 12 inc.

In the form shown in Figs. i, it and 9 a tubular body it, similar tobody 8 is employed, and ter= minals 4, identical with thwe previouslydescribed and inserted in the same manner in the bore '5'! of such body,are utilimd. However, instead of applying a graphite or other coating tothe interior surface of such bore in order to provide the desiredresistance connection between such terminals, a fine wire it? is woundhelically about the outer cylindrical surface of said body, the ends ofthe wire being secured to the respective terminals 6 by being woundclosely therearound adjacent the shoulders i3 thereon prior to suchterminals being forced into their final positions 7 in the body. Theconvolutions of the wire I? are of course spaced 9. sufliclent distanceapart to avoid any electrical connection therebetween, and in order thatthey will be held in place the body ii is formed with one or morenotches It so that the wire at the corresponding end may be engaged inone such notch (see Fig. 9). In order further to insure againstdisplacement of the convolutions of wire i2 a cylindrical sheath M ofinsulating material is slipped over the same. Such sheath (see Fig. 8)extends a short distance beyond each end of body it and the spacebetween such projecting ends and the shoulders 6 on terminals d isfilled in with plastic insulating material lb, thin providing in effecta close fitting case for the assembled unit, in its entirety. I

' The form of'the device illustrated in Figs. 19 and lldiiiers from thatjust described merely in that thebody IQ of the unit is formed at eachend with an enlarged head or flange I? in which notches l8 are providedto catch and hold the corresponding end of the wire l2. The constructionotherwise, including the manner in which the unit as a whole is encased,is exactly the same as in the form shown in Figs. 8 and e and the samereference numerals are applied to corresponding parts.

Fig. 12 illustrates a further modification of the form of the deviceshown in Figs. 1c and 11 in that instead or fitting a sheath is over theunit a layer is oi insulating plastic material is applied directly tothe outer surface of the body it so as to completely fill the spacebetween the heads ii and embed the convolutions of the wire is that ishelically wound upon such body. It desired. such plastic material mayalso be applied to the ends of the body so as to encase the same,together with the shoulders 6 on the respective terminals 4, in the samemanner as is illustrated in Figs. 7 and 8.

As previously indicated, my improved resistance unit, and particularlythe forms thereof illustrated in Figs. 1 to 6 inc., are readily adaptedfor automatic or semi-automatic assembly, and in Figs. 13 to 1'7 inc.there is diagrammatically shown an apparatus for carrying out suchmanu-. facture. The main element of such apparatus consists of arotatable disc 20 to which intermittent rotative movement may beimparted,.as by means of a pawl and ratchet mechanism 2i, the amount ofeach such movement corresponding with the distance between a series ofequally spaced transverse grooves 22 provided in the peripheral surfaceof said disc. The width of the latter is somewhat less than the lengthof the body l of the particular unit to be assembled. and as the discrotates successive such bodies are supplied to successive slots 22 froma chute 28 or other suitable feed mechanism. As shown in Fig. 13, thebodies are thus fed to the slots as they approach their uppermostposition in the course of rotation of the disc so that said bodies willremain under gravity where placed, and so be carried by the disc intoposition to be operated upon by the successive instrumentalities whichwill now be described.

Located at a suitable distance beyond the station where the bodies arethus supplied to the disc, and likewise themselves spaced 0. suitabledistance apart, are the two similar mechanisms illustrated in Figs. 1aand 15 whereby the coat ing is applied to the interior bores of thebodies. These mechanisms are identical except that one operates from oneside and the other from the opposite side of the body 6 as the latter isbrought into alignment therewith. nism comprises a stationary containerin which is maintained a body of the liquid coating composition,suchcontainer (see Fig. 15) having apertures 26 in its respective sidewalls which are aligned with the bore 2 of the body 5 when brought inproper position in relation to the mechanism by the step-by-steprotation ct disc 28. Extending through such apertures 25 is a rotatablefluted rod which may conveniently consist of a twist drill of properlength and of a di ameter such as will permit it to enter the bore 2 ofbody i and leave just sent space for a coating of desired thickness tobe applied to the surface of such bore. element ill is connected with asmall electric motor 2b which is mounted for reciprocable movementtransversely of disc 26. It will be understood that suitable operativeconnections, which need not be described in detail, are provided betweena slide 28 which carries each such motor and corresponding drill and thedisc 20, so that the reciprocating movement of the drills will be 75properly timed in relation to the step-by-step ro- Each such mecha= Eachsuch drill-like tative movement of said disc to bring a body Isuccessively in alignment with a drill located first opposite one endand then opposite the other end of said body. Thereupon the drills,while rapidly rotating, are advanced through the liquid composition inthe corresponding containers 25 into and through the bore 2 of body I.As a. result a very uniform application of the coating material to thesurface of such bore is obtained.

The remaining operation, that of inserting the terminals 4, is carriedout by the mechanism i1- lustrated in Figs. 16 and 17 which may belocated at any point beyond the station occupied by the last of the twocoating mechanisms. However, as shown in Fig. 13, such location shouldbe adjacent the upper portion of the disc so that the bodies Isuccessively brought into operative relation thereto will still remainin place in the transverse grooves 22 in the disc. The mechanism inquestion comprises simply two similar jaws or holders 30 mounted ontransversely reciprocable slides 3|, one on one side and the other onthe other side of the disc. Each such jaw or holder is formed to receivea corresponding terminal 4 and engage the shoulder 6 thereon. Theterminals are thus inserted in the jaws or holders when the latter arein their retracted positions. Thereupon when a body 1 is brought intoalignment with the terminals thus held, the two slides aresimultaneously moved toward each other, by means of picker andcylindrical actuators 32 controlled through suitable connections 33which effect such operation in timed relation to the step-bystepmovement of the .disc 20. Upon retraction of the slides the terminalsthus inserted in the inoperative ends of the body are left properlyplaced and firmly secured thereto so that upon the further rotation ofthe disc the body may be discharged therefrom. Such discharge will occurby the body simply dropping out of the slot when the latter reaches theproper inclination.

The modified construction of resistance unit illustrated in Figs. 7 to12 does not lend itself so readily to automatic assembly. However, inFig. 18 there is illustrated one convenient method for effectingassembly of such unit. As there shown, the terminals 4 are initiallyinserted only part way into the bore 2 of body I so as to leave theshoulders 6 on said terminals spaced a short distance from therespective ends of the body. A forked member 35 is then inserted betweenthe shoulder on one such terminal and the adjacent body end, while theend of the wire I2 is Wound around the opposite terminal adjacent theshoulder thereon. Next, such last-mentioned terminal is forced into itsfinal position, thus firmly securing the end of the wire in place. Thenthe wire is wound upon the body so as to provide the requisite number ofturns, and upon withdrawing member 35 it is finally wound around theother terminal adjacent the shoulder thereon. Such last-mentionedterminal is then forced into its final position and this portion of theassembly operation is completed.

As previously indicated, the provision of the upset shoulders 6 on theterminals 4 is desirable inasmuch as they serve as stops to limit theinward movement of the terminals when inserted in the bore of theinsulating body 5 and thus determine accurately the longitudinal extentof the coating of resistance conducting material applied to the surfaceof such bore. Furthermore, such shoulders facilitate the insertion ofthe terminals by means such as have been herein-before described.However, absent such shoulders, the terminals may still be inserted byother means which will control the extent to which they enter therespective ends of the bore and thus equally accurately gauge thelongitudinal extent of the intervening coating which constitutes theresistance element in the unit.

Other modes of applying the principle oi. my invention may be employedinstead of the one explained, change being made as regards the productand method herein disclosed, provided the step or steps stated by any ofthe following claims or the equivalent of such stated step or steps beemployed.

I therefore particularly point out and distinctly claim as my invention:

1. A resistance unit comprising a tubular member of insulating material,resistance conducting material applied in the form of a coating to thesurface of the bore of said member, and wire terminals inserted in therespective ends of said member and electrically connected with saidresistance material, said terminals having serrated engagement with suchbore.

2. A resistance unit comprising a tubular member of insulating material,resistance conducting material applied in the form of a coating to thesurface of the bore of said member, and wire terminals inserted in therespective ends of said member and electrically connected with saidresistance material, said terminals having serrated engagement with suchbore and having shoulders adapted to contact with the corresponding endsof said member and act as stops.

3. In the manufacture of resistance units of the type wherein a coatingof resistance conducting material is applied to the interior of atubular member of insulating material, the step which comprisesinserting into and withdrawing from the bore of said member, first oneend then the other thereof, a rotating fluted rod carrying suchmaterial.

WILBUR- M. KOHRING.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 540,073 Reed May 28, 18951,208,756 De Khotinsky Dec. 19, 1916 1,739,256 Pender et al. Dec. 10,1929 1,796,338 Moore Mar. 17, 1931 1,857,769 Silberstein May 10, 19322,087,736 Pugh July 20, 193'! 2,150,404 Schafer Mar. 14, 1939

